Vacuum insulating glass (VIG) units typically include at least two spaced apart glass substrates that enclose an evacuated or low-pressure space/cavity therebetween. The substrates are interconnected by a peripheral edge seal and typically include spacers between the glass substrates to maintain spacing between the glass substrates and to avoid collapse of the glass substrates that may be caused due to the low pressure environment that exists between the substrates. Some example VIG configurations are disclosed, for example, in U.S. Pat. Nos. 5,664,395, 5,657,607 and 5,902,652, the disclosures of which are all hereby incorporated by reference herein in their entireties.
FIGS. 1 and 2 illustrate a typical VIG unit 1 and elements that form the VIG unit 1. For example, VIG unit 1 may include two spaced apart glass substrates 2, 3, which enclose an evacuated low-pressure space/cavity 6 therebetween. Glass sheets or substrates 2,3 are interconnected by a peripheral edge seal 4 which may be made of fused solder glass, for example. An array of support pillars/spacers 5 may be included between the glass substrates 2, 3 to maintain the spacing of substrates 2, 3 of the VIG unit 1 in view of the low-pressure space/gap present between the substrates 2, 3.
A pump-out tube 8 may be hermetically sealed by, for example, solder glass 9 to an aperture/hole 10 that passes from an interior surface of one of the glass substrates 2 to the bottom of a recess 11 in the exterior surface of the glass substrate 2. A vacuum is attached to pump-out tube 8 to evacuate the interior cavity 6 to a low pressure, for example, using a sequential pump down operation. After evacuation of the cavity 6, the tube 8 is melted to seal the vacuum. Recess 11 retains the sealed pump-out tube 8. Optionally, a chemical getter 12 may he included within a recess 13 that is disposed in an interior face of one of the glass substrates, e.g., glass substrate 2. The chemical getter 12 may be used to absorb or hind with certain residual impurities that may remain after the cavity 6 is evacuated and sealed.
VIG units with fused solder glass peripheral edge seals 4 are typically manufactured by depositing glass frit, in a solution (e.g., frit paste), around the periphery of substrate 2. This glass frit paste ultimately forms the glass solder edge seal 4. A second substrate 3 is brought down on substrate 2 so as to sandwich spacers/pillars 5 and the glass frit solution between the two substrates 2, 3. The entire assembly including the glass substrates 2, 3, the spacers or pillars 5 and the seal material (e.g., glass fit in solution or paste), is then heated to a temperature of at least about 500° C., at which point the glass frit melts, wets the surfaces of the glass substrates 2, 3, and ultimately forms a hermetic peripheral or edge seal 4.
After formation of the edge seal 4, a vacuum is drawn via the pump-out tube 8 to form low pressure space/cavity 6 between the substrates 2, 3, The pressure in space 6 may be produced by way of an evacuation process to a level below atmospheric pressure, e.g., below about 10−2 Torr. To maintain the low pressure in the space/cavity 6, substrates 2, 3 are hermetically sealed. Small high strength spacers/pillars 5 are provided between the substrates to maintain separation of the approximately parallel substrates against atmospheric pressure. As noted above, once the space 6 between substrates 2, 3 is evacuated, the pump-out tube 8 may be sealed, for example, by melting using a laser or the like.
As a result of the process used to manufacture the VIG, including those used to form the seal 4 discussed above, residual hydrocarbons and/or polymers, such as, for example, solvents and binders used for making the frit paste that ultimately forms the seal between the transparent glass substrates of the VIG unit, may remain in the vacuum cavity. It is desirable to remove these residuals, as they have a potentially damaging effect on the VIG unit over time. For example, residual hydrocarbons and/or polymers may contaminate the vacuum cavity after the VIG is sealed (e.g., by producing volatile COX gases that degrade vacuum levels), and thereby continuously degrade the insulating value (e.g., R-value) of the VIG unit. The residual hydrocarbons may also react with coatings, such as, for example, a low-E coating that may be present on an interior surface of one of the glass substrates that form the vacuum cavity, further damaging performance of the VIG unit.
As mentioned above, VIG units with fused solder glass edge seals 4 are typically manufactured by depositing glass frit, in a solution (e.g., frit paste), around the periphery of substrate 2. This glass frit ultimately forms the glass solder seal 4. A second substrate 3 is brought down on substrate 2 so as to sandwich spacers/pillars 5 and the glass frit solution between the two substrates 2, 3. The entire assembly including the glass substrates 2, 3, the spacers/pillars 5 and the seal material (e.g., glass frit in solution), is then heated to a temperature of at least about 500° C., at which point the glass frit melts, wets the surfaces of the glass substrates 2, 3, and ultimately forms a hermetic seal 4. An advantage of providing this high-temperature processing is that much of the residual hydrocarbon and/or polymer compounds, such as, for example, the binders and solvents used to make the frit paste for the solder glass seal 4, are oxidized or burned off during this process and are then removed from the vacuum cavity prior to sealing.
However, a new class of materials are being developed for use in forming hermetic edge seals for VIG units. For example, a vanadium inclusive seal composition is disclosed in U.S. patent application Ser. No. 13/354,963, entitled, “Coefficient of Thermal Expansion Filler for Vanadium-Based Frit Materials and/or Methods of Making and/or Using the Same,” filed Jan. 20, 2012, the disclosure of which is incorporated by reference herein in its entirety. These new seal compositions may sometimes be referred to as VBZ (e.g., vanadium, barium, zinc) based compositions. These vanadium inclusive and/or VBZ type seal compositions provide certain advantages over other known seal compositions. However, when using VBZ type seal compositions, a lower temperature sealing thermal profile is used to maintain the desired temper of the glass of the VIG unit because VBZ compositions have a lower firing temperature (e.g., <250° C.) than certain other conventional glass frit compositions used to form seals in VIG units. One example reason for using lower firing temperatures to make VIG units using, for example, a VBZ seal, is that VBZ seal compositions may begin to soften at the higher temperatures (e.g., 300° C.-350° C.). As a result of this softening, gases being evolved during the burning of residual carbon compounds become entrapped in the VBZ material. This causes expansion of the softened VBZ material and results in a porous glass having insufficient strength and which cannot hold a vacuum. The lower thermal profile used to form a VBZ type seal is such that the normal high-temperature burn out procedure described above regarding fused solder glass seals 4 to oxidize and burn off residual hydrocarbons and polymers cannot be used. The lower seal curing temperature(s) used to cure/form the edge seal, when the seal is made of a vanadium inclusive and/or VBZ material, are insufficient to provide acceptable burn off of residual hydrocarbons and polymers.
Therefore, what is needed is a lower temperature method to rapidly decompose the residual hydrocarbons and/or polymers in the cavity of the VIG unit in at least situations that use lower temperature profile edge seal compositions, such as, for example, and without limitation, vanadium based and/or VBZ, type seal compositions. As discussed above, with the development of newer seal compositions, such as, for example, and without limitation, vanadium based and/or VBZ type seal compositions, a new lower temperature sealing thermal profile is generally used to maintain desired temper strength of the glass substrates of the VIG unit and/or to maintain the structural stability and vacuum maintaining properties of the resulting seal. As further noted above, the lower temperature cycle is not typically sufficient to sufficiently remove and/or burn off a sufficient amount of residual hydrocarbons and polymers, such as, for example, and without limitation, from the solvent and binder materials used for making the edge seal paste. The hydrocarbon and/or polymer residue in the interior of the VIG vacuum cavity may contaminate the vacuum once the VIG unit is sealed, and may further degrade various coatings that may be present on interior surfaces of the glass substrates used in the VIG units. For example, in certain instances residual carbon that coats the internal surface of the glass substrate(s) may remain, such as, for example, with a thin monolayer of hydrocarbons and binder polymer. This carbon residue may detach from the interior surface of the glass over time and decompose under ultraviolet radiation of sunlight and produce volatile, for example, COX gases which degrade the vacuum levels and adversely decrease the insulating value (e.g., R-value) of the VIG unit. Additionally, the residual carbons may, over time, react with coatings on the interior glass surface, such as, for example, low-E coatings, further degrading performance of the VIG unit.
To solve these and/or other drawbacks, a new cleaning process to remove residual hydrocarbon compounds is disclosed and described herein with reference to certain example embodiments. For example, according to certain example embodiments, including ozone (O3) as a component of a purge gas used during initial pump down has been found to oxidize carbon compounds and convert them to more volatile CO and/or CO2 that may then be easily removed through sequential pump down operations and may be even further diluted by optional sequential N2 purging and a final deep vacuum pull down. The removal of these residual carbon compounds enhances the overall performance of VIG units by, for example, and without limitation, enhancing the overall insulating value (e.g., R-value), imimproving the useful life of the VIG unit and/or reducing degradation of optional coatings that may be used on an interior surface of the glass substrates of the VIG unit.
According to certain example embodiments, an example method of decomposing residual carbon for removal from the vacuum cavity of a VIG window unit is provided, wherein at least an ozone (O3) and oxygen (O2) gas mixture is introduced into the VIG vacuum cavity during and/or before an initial stage of a vacuum pump down process. According to certain example embodiments, a small percentage of O3, such as, for example, and without limitation, in a range of about from 5-10 wt. % ozone, is generated using, for example, an ozone generator using air and/or pure oxygen. The resulting O3/O2 mixture is then introduced into the vacuum cavity of the VIG under reduced pressure, allowed to react with the residual hydrocarbons and/or polymers, and then removed from the cavity by, for example, a vacuum pump. A cycle of O3/O2 purges may be repeated as necessary to reduce the contaminants to suitable or acceptable levels. Example acceptable contaminant levels may be, for example, and without limitation, from about 10E-12 or lower. It will he understood that acceptable contaminant levels may be determined or selected by the manufacturer.
It is also noted that the ozonization of the vacuum cavity of the VIG unit described above may performed at substantially ambient temperatures thereby avoiding the disadvantages and problems associated with high-temperature processing, especially for example when using newer seal compositions, such as, for example, vanadium inclusive and/or VBZ type seal compositions. It may sometimes be the case that additional energy may be used to facilitate and/or improve the carbon removal achieved by the ozonization process described above. Thus, it is contemplated that additional energy in the form of, for example, and without limitation, elevated temperatures (remaining below levels that might adversely affect the seal composition; e.g., remaining below about 250 degrees C.), radio frequency (RF) plasma, corona discharge (electric fields), UV lamp, and/or the like, may be used to increase reaction rates of the residual hydrocarbons and/or polymers and the ozone.
According to certain further example embodiments, the resulting trace amounts of volatile carbons that may remain, even after an ozonization process such as, for example, may be further diluted by sequential N2 purging and/or a final deep vacuum pull down. Using an ozonization process along the lines described by way of example above, facilitates removal of residual carbon compounds, improves the overall lifetime of a VIG window unit, provides a more stable and predictable R-value and helps maintain coatings that may be present on the surface of the glass substrate in the vacuum cavity.
These and other advantages are provided by a method for cleaning a vacuum cavity of a VIG window unit comprising: providing a vacuum insulated glass window unit including a vacuum cavity; generating a cleaning gas mixture comprising ozone; pumping the cleaning gas mixture comprising ozone into the vacuum cavity of the vacuum insulated glass window unit; maintaining the cleaning gas mixture comprising ozone in the vacuum cavity of the vacuum insulate glass window unit for a dwell time; and removing compounds created by a reaction of the cleaning gas mixture, and residual cleaning gas from the vacuum cavity.
According to certain example embodiments, there is provided an apparatus comprising: an ozone generator; a bi-directional pump operatively coupled to said ozone generator and operatively coupled to a pump-out tube, said pump-out tube providing access to a cavity between first and second substrates; and a gas source providing a gas including oxygen to the ozone generator, wherein said bi-directional pump pumping the cleaning gas mixture comprising ozone generated by the ozone generator into the cavity, maintaining the cleaning gas mixture comprising ozone in the cavity for a predetermined dwell time, and removing compounds created by reaction of the cleaning gas mixture and residual cleaning gas from the cavity
These and other embodiments and advantages are described herein with respect to certain example embodiments and with reference to the following drawings in which like reference numerals refer to like elements, and wherein: